/*
 * Copyright (c) 2011-2015 Pivotal Software Inc., Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.camunda.bpm.extension.reactor.projectreactor.queue.internal;

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

import org.camunda.bpm.extension.reactor.projectreactor.internal.PlatformDependent;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

public abstract class MpscLinkedQueueNode<T> {

  @SuppressWarnings("rawtypes")
  private static final AtomicReferenceFieldUpdater<MpscLinkedQueueNode, MpscLinkedQueueNode> nextUpdater;

  static {
    @SuppressWarnings("rawtypes")
    AtomicReferenceFieldUpdater<MpscLinkedQueueNode, MpscLinkedQueueNode> u;

    u = PlatformDependent.newAtomicReferenceFieldUpdater(MpscLinkedQueueNode.class, "next");
    if (u == null) {
      u = AtomicReferenceFieldUpdater.newUpdater(MpscLinkedQueueNode.class, MpscLinkedQueueNode.class, "next");
    }
    nextUpdater = u;
  }

  @SuppressWarnings("unused")
  private volatile MpscLinkedQueueNode<T> next;

  final MpscLinkedQueueNode<T> next() {
    return next;
  }

  final void setNext(final MpscLinkedQueueNode<T> newNext) {
    // Similar to 'next = newNext', but slightly faster (storestore vs loadstore)
    // See: http://robsjava.blogspot.com/2013/06/a-faster-volatile.html
    nextUpdater.lazySet(this, newNext);
  }

  public abstract T value();

  /**
   * Sets the element this node contains to {@code null} so that the node can be used as a tombstone.
   */
  protected T clearMaybe() {
    return value();
  }

  /**
   * Unlink to allow GC'ed
   */
  void unlink() {
    setNext(null);
  }
}
